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RARE ANT MAY HELP
SOLVE SOME MYSTERIES OF SOCIAL EVOLUTION

COLUMBUS, Ohio – Last fall, ecologists at Ohio State University
cracked open an acorn they had found in an Ohio park and discovered a
colony of extremely rare ants.

They had uncovered Leptothorax
minutissimus, an ant species that has been found in only four
other areas of the eastern United States. The researchers found the acorn
at a Columbus metro park – the first time the ant has been found
in Ohio.

L. minutissimus is a unique social parasite in that it lives
entirely within the colonies of other ant species. But unlike parasitic
slave-maker ants, which raid and virtually destroy the colonies of unsuspecting
hosts, L. minutissimus appears to move in and live amiably with
its host. Such organisms are called inquilines.

This relationship intrigues Herbers, who is planning a new study to
learn more about these unique ants.

The first and only written description of L. minutissimus is
from 1942, when researchers found a colony in Washington, D.C. Since then,
colonies have been found at sites in West Virginia, Indiana and on Long
Island. And these colonies of anywhere from 50 to 100 ants thrive in the
tiniest places – old acorns, hickory nuts, hollow twigs and grasses.

These tiny ants that grow to around 3 millimeters long – about
the length of the writing tip of a ball point pen – are a rich golden
color. But it's how they interact with their hosts that make them a real
scientific find. Studying these behaviors closely may give researchers
insight into some of the riddles of social evolution.

These
tiny ants that grow to around 3 millimeters long – about the
length of the writing tip of a ball point pen – are a rich
golden color. But it's how they interact with their hosts that make
them a real scientific find. Studying these behaviors closely may
give researchers insight into some of the riddles of social evolution.

While L. minutissimus is a parasite, it doesn't appear to stage
the bloodthirsty coups common to its slave-maker ant relatives. Rather,
it behaves much like the unwelcome in-laws who come to visit for an undetermined
length of time. Numerous L. minutissimus queens move into a new
colony and attach themselves to host queens.

But researchers aren't sure how L. minutissimus moves from
colony to colony, as it apparently lacks the worker ants that, in other
species, are responsible for scouting out new dwellings.

"L. minutissimus is highly specialized because it's lost
its worker caste through evolution," Herbers said. Researchers believe
this to be true because no L. minutissimus slave-making worker
ants have ever been found.

In slave-making ant species, specialized workers raid colonies to secure
the labor force needed to forage for food, care for the queen and so on.
Slave-makers therefore rely on overt aggression to make a living, but
L. minutissimus is apparently accepted into host colonies without
any violence.

Assuming that slave-making worker ants are solely responsible for finding
new colonies has left researchers wondering how L. minutissimus
queens travel from colony to colony.

"Perhaps these queens go out and mate and find colonies that way,"
Herbers said. "But we just don't know."

During mating season, ant queens grow wings in order to fly around and
find males. The wings either fall off or are bitten off by the queen once
mating is over.

"We think that the L. minutissimus ants are even more
highly evolved than slave-making ants simply because these queens seem
to get by quite well on their own," Herbers said. "The fundamental
question we hope to answer is what happens in an evolutionary sense as
the interactions between parasites and hosts proceed over time."

This summer, Herbers and her colleagues will conduct laboratory experiments
comparing the behavior of L. minutissimus to two species of slave-making
ants. Each parasite will have a chance to move into a colony of a fairly
common host species, Leptothorax
curvispinosus.

"We're going to look at the impact each parasite has on the host,"
Herbers said, adding that each species will be housed in separate plastic
boxes. A filter paper bridge will connect boxes of parasitic ants to boxes
of host ants.

The researchers will also put the parasitic species in groups of two
and three and let them loose on the host. The idea is to see how and if
the parasites interact with each other, and who dominates in those interactions.

"Slave-maker behavior ranges from the all-out ruthless and bloody
annihilation of another ant colony to slave-maker ants that have a more
harmonious relationship with their host," Herbers said. "We
want to know what separates the behavior of one species from another,
what makes one more ruthless than another, and to see if we can get more
insight into the key evolutionary differences between these parasitic
ants."